1. Field of the Invention
The present invention concerns a method to generate a homogenous radio-frequency field in a spatial examination volume of a magnetic resonance system for the examination of a subject wherein the magnetic resonance system has a body coil (composed of a number of resonator segments with conductor elements arranged around the examination volume, parallel to the longitudinal axis of a base field magnet) and a control and evaluation device to separately control the individual resonator segments electromagnetically decoupled from one another.
2. Description of the Prior Art
Magnetic resonance tomography are imaging methods for medical diagnostics that uses the interaction of an external field (here a magnetic field) with the human body for imaging. The general design and the functioning of such a magnetic resonance system are known and need not be described in detail herein.
Magnetic resonance systems have been conventionally used in which the basic magnetic field is more than 1.5 T, in particular 3 T and more. Better resolutions are achievable with these magnetic resonance systems, but additional inhomogeneities of the image quality occur in such conventional systems that are traced back to inhomogeneities in the excitation field generated by the body coil.
It is known from U.S. Pat. No. 6,252,403 to fashion the transmission antenna in the shape of a spiral in order to compensate for radio-frequency eddy currents that lead to inhomogeneities. The transmission antenna thus assumes the appearance of a birdcage resonator wound around a symmetry axis. From this document, it is also known to arrange suitable dielectrics, in particular water, in proximity to the examination subject in order to hereby achieve a homogenization of the radio-frequency excitation field. Despite these features a sufficient compensation of the inhomogeneities in the body coil excitation field is not possible in all cases.
Furthermore, from European Application 1 279 968, discloses a magnetic resonance system in which resolution segments that are electromagnetically decoupled from one another and that form a body coil are provided according to the system design previously specified. Here the individual resolution segments can oscillate at the desired resolution frequency independently of one another. A separate transmission channel is associated with each resonator segment, meaning that each resonator segment can be separately activated, enabling the generation of separate individual fields that collectively produce a circularly polarized radio-frequency field. The amplitude and the phase of each transmission channel can be individually set.